import PySimpleGUI as sg

"""
    Demo - Drag a rectangle to draw it

    This demo shows how to use a Graph Element to (optionally) display an image and then use the
    mouse to "drag a rectangle".  This is sometimes called a rubber band and is an operation you
    see in things like editors
"""


# image_file = r'Color-names.png'
image_file = None       # image is optional

layout = [[sg.Graph(
            canvas_size=(400, 400),
            graph_bottom_left=(0, 400),
            graph_top_right=(400, 0),
            key="-GRAPH-",
            change_submits=True,  # mouse click events
            drag_submits=True),],
            [sg.Text("", key="info", size=(60, 1))]]

window = sg.Window("draw rect on image", layout, finalize=True)
# get the graph element for ease of use later
graph = window["-GRAPH-"]     # type: sg.Graph

graph.DrawImage(image_file, location=(0,0)) if image_file else None
dragging = False
start_point = end_point = prior_rect = None

while True:
    event, values = window.Read()
    if event is None:
        break  # exit
    if event == "-GRAPH-":                      # if there's a "Graph" event, then it's a mouse
        x, y = values["-GRAPH-"]
        if not dragging:
            start_point = (x, y)
            dragging = True
        else:
            end_point = (x, y)
        if prior_rect:
            graph.DeleteFigure(prior_rect)
        if None not in (start_point, end_point):
            prior_rect = graph.DrawRectangle(start_point, end_point, line_color='red')
    elif event.endswith('+UP'):                 # The drawing has ended because mouse up
        info = window.Element("info")
        info.Update(value=f"grabbed rectangle from {start_point} to {end_point}")
        start_point, end_point = None, None     # enable grabbing a new rect
        dragging = False
    else:
        print("unhandled event", event, values)
